Correcting device, exposure apparatus, device production method, and device produced by the device production method

ABSTRACT

A correcting device that properly maintains the flatness of a mask, an exposure apparatus in which overlay accuracy is increased by making use of the correcting device, and a device production method. The correcting device includes a gas flow path including a first area and a second area. The first area is formed above a reticle having formed thereon a pattern that is projected onto a material to be processed in order to form an image of the pattern on the material to be processed. The second area is connected to the first area, has a cross-sectional area that is different from that of the first area, and is not disposed in line with the reticle. The correcting device also includes a blowing section that blows gas to the gas flow path.

BACKGROUND OF THE INVENTION

1. Field of the Invention

In general, the present invention relates to an exposure apparatus. Moreparticularly, the present invention relates to an exposure apparatusused to expose a material to be processed, such as a monocrystallinesubstrate for a semiconductor wafer or a glass substrate for a liquidcrystal display (LCD), a correcting device that corrects deformation ofa mask or a reticle (hereafter, these terms are used interchangeably inthe application) used in the exposure apparatus, a device productionmethod using the material to be processed, and a device that is producedfrom the material to be processed. The present invention is, forexample, suitable for application to an exposure apparatus which exposesa monocrystalline substrate for a semiconductor wafer by thestep-and-scan projection method, the scan projection method, or thestep-and-repeat projection method in a photolithography process.

Here, the step-and-scan projection method is a projection exposuremethod in which a wafer is continuously scanned in synchronism with ascanning movement of a mask or a reticle in order to project a patternof the mask onto the wafer by exposure, after which, after completion ofan exposure of one shot, the wafer is moved stepwise in order to movethe next shot to an exposure area. The scan projection method is aprojection exposure method in which a portion of the mask pattern isprojected onto the wafer by a projection optical system and the mask anda material to be processed are scanned in synchronism with each otherwith respect to the projection optical system in order to project thewhole mask pattern onto the wafer by exposure. The step-and-repeatprojection method is a projection exposure method in which the wafer ismoved stepwise with each full exposure of a shot of the wafer in orderto move the next shot to the exposure area.

2. Description of the Related Art

In recent years, the demand for smaller and thinner electronic deviceshas caused an increasing demand for finer semiconductor devicesinstalled in the electronic devices. For example, it is expected thatdesign rules of a mask pattern will become increasingly smaller in thefuture as a result of an attempt to realize a line and space (L & S) of130 nm in a mass production line. L & S refers to an image projectedonto a wafer during exposure with the widths of the lines and spacesbeing equal, so that it is a measure of exposure resolution. In theexposure, resolution, overlay accuracy, and throughput are threeimportant parameters. Resolution is defined as the smallest dimensionthat can be precisely transferred. Overlay accuracy is defined as theaccuracy with which several patterns are overlaid on a material to beprocessed. Throughput is the number of materials that are processed perunit time.

There are basically two types of exposure methods, a 1× magnificationtransfer method and a projection method. The 1× magnification transfermethod includes a method in which a mask and a material to be processedare brought into contact with each other and a method in which they areseparated slightly. However, in the former method, although a highresolution can be obtained, the mask gets damaged and the material to beprocessed gets scratched or defective due to dust or pieces of siliconbeing pressed into the mask. In the latter method, the problem thatexists in the former method is initially solved, but, when theseparation between the mask and the material to be processed becomessmaller than the maximum size of dust particles, damage to the masksimilarly occurs.

To overcome the problem that the mask and the material to be processedbecome damaged, a projection method in which the mask and the materialto be processed are further separated has been proposed. Of thedifferent types of projection methods, the projection method that uses ascanning projection exposure apparatus is in dominant use in recentyears in order to improve resolution and to increase the size of anexposure area. In this projection method, the mask is exposed a portionat a time, and the mask and the wafer are caused to be in synchronismwith each other. By scanning the wafer either continuously orintermittently, the entire mask pattern is projected onto the wafer byexposure.

In general, a projection exposure apparatus comprises an illuminationoptical system that illuminates a mask and a projection optical system,disposed between the mask and a material to be processed, which projectsa circuit pattern of the mask that has been illuminated onto thematerial to be processed. In the illumination optical system, in orderto obtain a uniform illumination area, light beams from a light sourceare made to enter a light integrator comprising, for example, fly's eyelenses that are provided using a plurality of rod lenses. With alight-exiting surface of the light integrator being used as a secondarylight source surface, these light beams that have entered the lightintegrator are used to subject a mask surface to Koehler illuminationthrough a condenser lens.

However, when the optical axis substantially coincides with thedirection of gravitational force, the center portion of the mask isflexed by an amount on the order of a few microns in the direction ofthe gravitational force due to its own weight, resulting in a problemthat overlay accuracy is reduced during the exposure. More specifically,the following problems arise: (1) Distortion of a projected image of thepattern changes as a result of distortion of the mask pattern, and (2)focal depth, which is the focal range that allows a certainimage-formation performance to be maintained, is reduced by curvature offield. In particular, it is expected that due to the recent demand forfiner patterns, even a slight variation in the pattern must beincreasingly taken into account in the future.

To overcome such problems, Japanese Patent Laid-Open No. 10-214780proposes, in a first embodiment, to enclose a mask in order to applystatic pressure to a hermetically sealed space through a pressurecontrol device. However, when the mask is enclosed, heat produced byexposure causes the mask to be distorted, so that this method is not apreferable method. In addition, the same document proposes, in a secondembodiment, to correct the distortion of the mask through apiezoelectric device disposed around the mask. However, the use of thepiezoelectric device around the mask is not necessarily effective inremoving flexure of the center portion of the mask caused by its ownweight.

Japanese Patent Laid-Open No. 6-176408 proposes to supply gas having apredetermined pressure to a mask from a direction opposite to thedirection in which the mask flexes. However, it is difficult touniformly apply pressure to the mask. In addition, it is difficult todispose gas blowing means while maintaining an exposure optical system.

SUMMARY OF THE INVENTION

In general, it is an object of the present invention to provide a novel,useful correcting device, exposure apparatus, device production method,and device produced by the production method, which make it possible toovercome these conventional problems.

More specifically, it is an object of the present invention to provide,for illustrative purposes, a correcting device that properly maintainsthe flatness of a mask, and an exposure apparatus and a deviceproduction method, which make it possible to increase overlay accuracyby making use of the correcting device.

It is another object of the present invention to provide, as fordifferent illustrative purposes, devices, such as a high-qualitysemiconductor, a liquid crystal device (LCD), a charge-coupled device(CCD), and a thin-film magnetic head, which are produced by the deviceproduction method.

To overcome the above-described problems, according to a first aspect,the present invention provides a correcting device comprising a gas flowpath including a first area and a second area, the first area beingformed above a reticle having formed thereon a pattern that is projectedonto a material to be processed in order to form an image of the patternon the material to be processed, and the second area being connected tothe first area, having a cross-sectional area that is different fromthat of the first area, and not being disposed in line with the reticle;and a blowing section that blows gas to the gas flow path.

According to this correcting device, by blowing gas (e.g., air ornitrogen) to a gas flow path having two continuously formed areas, suchas a first area and a second area, having different cross-sectionalareas, a difference in pressure between the first area and the secondarea can be produced by making use of Bernoulli's theorem. By properlymaking use of the pressure difference, the correcting device can correctdistortion caused by factors other than the self-weight of the reticle.In addition, the correcting device can restrict a rise in temperature ofthe reticle caused by exposure heat by cooling the reticle as a resultof blowing air onto it.

When a third area is provided upstream from the first area in terms ofthe gas that is blown, and when the cross-sectional area of the thirdarea is greater than the cross-sectional area of the first area, it ispossible to reduce the temperature of the gas in the first area, so thatthe rise in temperature of the reticle caused by the exposure heat canbe more efficiently reduced.

When the structure of the first aspect is used, the correcting devicemay further comprise a smoothing section, disposed between the first andsecond areas, for smoothing movement of the gas between the first andsecond areas. Accordingly, the smoothing section can prevent the gasfrom deviating from Bernoulli's theorem caused by the gas swirlingbetween the first and second areas. The gas flow path may be providedopposite to the material to be processed with regard to the reticle. Ingeneral, since a pellicle film is provided at the side of the materialto be processed, by providing the gas flow path opposite to the materialto be processed with regard to the reticle, it is possible to preventdeformation of and damage to the pellicle film caused by air blowingacross or onto the pellicle film.

When the structure of the first aspect is used, the correcting devicemay further comprise a control section that controls the blowing sectionso that, when the density of the gas is ρ, the weight of the reticle isG, the area of projection of the reticle is A_(R), the cross-sectionalarea of the first area is A₁, the pressure of the gas in the first areais P₁, the velocity is V₁, the cross-sectional area of the second areais A₂, and the pressure of the gas in the second area is P₂, thefollowing formula is satisfied:P ₁ −P ₂=0.5·ρ·V ₁ ²·{(A ₁ /A ₂)²−1}=−G/A _(R).By virtue of this structure, the correcting device can correct thedistortion caused by the self-weight of the reticle. P₂ may be set atatmospheric pressure. When the second area is set at atmosphericpressure and the space around the reticle is open, as disclosed in thefirst embodiment illustrated in Japanese Patent Laid-Open No. 10-214780,the exposure heat is no longer confined in the area around the recticle,so that the temperature rise of the reticle can be restricted.

According to a second aspect, the present invention provides acorrecting device comprising a blowing section that blows gas onto areticle having formed thereon a pattern to be projected onto a materialto be processed in order to form an image of the pattern on the materialto be processed; a detecting section that detects pressure at front andback surfaces of the reticle and produces a detection result; and acontrol section that controls the blowing section so that a differencebetween the pressures is maintained to be a predetermined value, afterreceiving the detection result provided by the detecting section. Thecorrecting device can correct the distortion of the reticle because thepressure difference at the front and back surfaces of the reticle iscontrolled by the control section so that it becomes a predeterminedvalue (for example, a value that cancels the deformation caused by theweight of the reticle due to gravitational force).

According to a third aspect, the present invention provides a correctingdevice comprising a blowing section that blows gas onto a reticle havingformed thereon a pattern to be projected onto a material to be processedin order to form an image of the pattern on the material to beprojected; a detecting section that detects a flexure amount of thereticle and produces a detection result; and a control section thatcontrols the blowing section so that the flexure amount is zero afterreceiving the detection result provided by the detecting section. Thecorrecting device can correct the distortion of the reticle becausefeedback is controlled by the control section so that the flexure amountof the reticle is zero.

The control sections of these correcting devices can, for example,control the gas speed and the temperature of the gas at the blowingsection.

According to a fourth aspect, the present invention provides an exposureapparatus comprising any one of the above-described correcting devices,an illumination optical system that illuminates the pattern, and aprojection optical system that projects the pattern onto the material tobe processed in order to form an image of the pattern on the material tobe processed. The exposure apparatus can provide the operations of anyone of the above-described correcting devices.

According to a fifth aspect, the present invention provides a method ofproducing a device comprising the steps of blowing gas to a gas flowpath including a first area and a second area, the first area beingformed above a reticle having formed thereon a pattern that is projectedonto a material to be processed in order to form an image of the patternon the material to be processed, and the second area being connected tothe first area, having a cross-sectional area that is different fromthat of the first area, and not being disposed in line with the reticle;subjecting the material to be processed to a projection exposureoperation using the reticle; and performing a predetermined processingoperation on the material that has been subjected to the projectionexposure operation. The device production method, which is carried outby the same operations as those of the exposure apparatus as a result ofthe blowing step, is used to provide devices, which are intermediate orfinal products. The device production method may further comprise thestep of detecting distortion of the reticle and the step of controllingthe blowing of the gas so that the distortion of the reticle is reducedbased on a result provided by the detection. By the control operationstep, the distortion of the reticle can be corrected with highprecision. Examples of such devices are semiconductor chips used, forexample, for large-scale integration (LSI) or very large-scaleintegration (VLSI), charge-coupled devices (CCDs), liquid crystaldevices (LCDs), magnetic sensors, and thin-film magnetic heads.

Further objects, features and advantages of the present invention willbecome apparent from the following description of the preferredembodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an exposure apparatus of an embodiment ofthe present invention.

FIG. 2 is a schematic, sectional view used to illustrate the principleof a correcting device of the exposure apparatus shown in FIG. 1.

FIG. 3 is a schematic, sectional view used to illustrate the principleof the correcting device of the exposure apparatus shown in FIG. 1.

FIG. 4 is a graph showing the relationship between upstream gaugepressure and upstream gas speed in the views shown in FIGS. 2 and 3.

FIG. 5 is a perspective view of a modification of the correcting deviceshown in FIG. 1.

FIG. 6 is a sectional view of the correcting device shown in FIG. 5.

FIG. 7 is an exploded perspective view used to illustrate a method ofsetting a reticle usable in the correcting device shown in FIG. 5.

FIG. 8 is a sectional view of another modification of the correctingdevice shown in FIG. 1.

FIG. 9 is a perspective view of still another modification of thecorrecting device shown in FIG. 1.

FIG. 10 is a sectional view of the correcting device shown in FIG. 9.

FIG. 11 is a perspective view of still another modification of thecorrecting device shown in FIG. 1.

FIG. 12 is a sectional view of still another modification of theexposure apparatus and of the correcting device shown in FIG. 1.

FIG. 13 is a sectional view showing a state in which the reticle hasmoved in the sectional view of FIG. 12.

FIG. 14 is a schematic, side view of the exposure apparatus shown inFIGS. 12 and 13.

FIG. 15 is an external perspective view of the exposure apparatus shownin FIG. 14.

FIG. 16 is a schematic block diagram of a detecting section that detectsdistortion of the reticle used in the exposure apparatus shown in FIG.1.

FIG. 17 is a flowchart used to illustrate a device production methodincluding an exposure step in accordance with the present invention.

FIG. 18 is a detailed flowchart of Step 4 shown in FIG. 17.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereafter, for illustrative purposes, an exposure apparatus 1 of thepresent invention will be described with reference to the attacheddrawings. FIG. 1 shows an optical path of a simplified optical system ofthe illustrative exposure apparatus 1 of the present invention.

As shown in FIG. 1, the exposure apparatus 1 comprises an illuminationdevice 10, a reticle 20, a projection optical system 30, a plate 40, anda correcting device 100. The exposure apparatus 1 is a scanningprojection exposure apparatus which, by exposure, projects a circuitpattern formed on the reticle 20 onto the plate 40 by thestep-and-repeat projection exposure method or the step-and-scanprojection exposure method.

The illumination device 10 illuminates the reticle 20 on which thecircuit pattern to be transferred is formed, and comprises a lightsource 12 and an illumination optical system 14.

For the light source 12, a laser may be used. For the laser, an ArFexcimer laser having a wavelength of approximately 193 nm, a KrF excimerlaser having a wavelength of approximately 248 nm, or an F₂ excimerlaser having a wavelength of approximately 153 nm may be used. However,the types of lasers which may be used are not limited to excimer lasers,so that, for example, a yttrium-aluminum-garnet (YAG) laser may be used.The number of lasers used is not limited. When a laser is used as thelight source 12, it is preferable to use a light-beam-shaping opticalsystem that shapes parallel light beams from the laser light source intobeams having desired forms and an optical system that converts coherentlaser light beams into incoherent light beams. The types of lightsources that can be used as the light source 12 are not limited tolasers, so that one or a plurality of mercury lamps, xenon lamps, etc.,may be used.

The illumination optical system 14 illuminates the mask 20, and includesa lens, a mirror, a light integrator, and a stop. For example, acondenser lens, a fly's eye lens, an aperture stop, a condenser lens, aslit, and an image-forming optical system are disposed in that order.The illumination optical system 14 is used regardless of whether thelight is axial or oblique light. Examples of the light integratorinclude integrators formed by placing fly's eye lenses or two sets ofcylindrical lens array (or reticular lens) plates upon each other. Thelight integrator may be replaced by an optical rod or a diffractingdevice.

A circuit pattern (or image) to be transferred is formed on the reticle20. Diffraction light coming from the reticle 20 is projected onto theplate 40 through the projection optical system 30. The plate 40 is amaterial to be processed, such as a wafer or a liquid crystal substrate,and has a resist coated thereto. The reticle 20 and the plate 40 are ina conjugate relationship. In the embodiment, an optical axis OO′ shownin FIG. 1 matches the direction of gravitational force. The reticle 20used in the embodiment is formed of quartz and has a density ofapproximately 2200 kg/m³, a size of 152 mm in the vertical direction×asize of 152 mm in the horizontal direction×a size of 6.35 mm in theheight direction, and a weight of 323 gf (=3.17 N), which isapproximately equivalent to a pressure of 140 Pa.

When a scanning projection exposure apparatus is used, the pattern onthe mask 20 is transferred onto the plate 40 by scanning the mask 20 andthe plate 40 in synchronism with each other. When a stepper (or anexposure apparatus using the step-and-repeat exposure method) is used,exposure is performed while the mask 20 and the plate 40 are stopped.

For the projection optical system 30, there may be used, for example, anoptical system comprising only a plurality of lens elements, an opticalsystem (catadioptric optical system) including a plurality of lenselements and at least one concave mirror, an optical system including aplurality of lens elements and at least one diffracting optical elementsuch as a saw-tooth shaped diffracting optical element, or an opticalsystem which is entirely a mirror may be used. When chromatic aberrationneeds to be corrected, the projection optical system 30 may be formedusing a plurality of lens elements formed of glass materials havingdifferent variances (Abbe numbers) or the diffracting optical elementmay be formed so that scattering occurs in a direction opposite to thelens elements.

The plate 40 is coated with a photoresist. The photoresist applying stepconsists of a pre-processing operation, an operation for applying anadhesiveness increasing agent, a photoresist applying operation, and apre-baking operation. The pre-processing operation includes cleaning,drying, and the like. The operation for applying an adhesivenessincreasing agent is carried out to modify the surface of the plate 40(that is, to increase its hydrophobic property by applying a surfaceactive agent), so that the adhesiveness between the photoresist and abase is increased. In the operation for applying an adhesivenessincreasing agent, an organic film, such as a hexamethyl-disilazane(HMDS) film, is applied or evaporated. The pre-baking operation is abaking operation, but provides a softer surface than that afterdevelopment, and is carried out to remove solvent.

The correcting device 100 corrects distortion or flexure of the reticle20. The reticle 20 is flexed due to its own weight by a few microns inthe direction of a gravitational force that is parallel to the opticalaxis OO′ shown in FIG. 1. Therefore, the correcting device 100 firstcorrects the distortion of the reticle 20 caused by its own weight bymaking use of Bernoulli's theorem. The correcting device 100 comprises agas pipe 110, which forms a gas flow path 111, and a blowing section120, which blows gas to the gas flow path 111. The gas flow path 111comprises an area 112, which is situated above or below the reticle 20,and an area 114, which is not situated in line with the reticle 20.

The principle of the correcting device 100 will be described withreference to FIGS. 2 and 3. Here, FIGS. 2 and 3 are schematic, sectionalviews used to illustrate the principle of the correcting device 100.FIG. 2 illustrates the case in which a gas flow path 111A is disposedbelow the reticle 20, and FIG. 3 illustrates the case in which a gasflow path 111B is disposed above the reticle 20. In FIGS. 2 and 3, thearrows represent the directions in which gas flows. The gas flow path111A (in FIG. 2) comprises a wide area 112A, which is disposed below thereticle 20, and a narrow area 114A, which is not in line with thereticle 20. The gas flow path 111B (in FIG. 3) comprises a narrow area112B, which is disposed above the reticle 20, and a wide area 114B,which is not in line with the reticle 20. Here, Formula 1 is establishedfrom Bernoulli's theorem: $\begin{matrix}{{{\frac{1}{2}V_{1}^{2}} + \frac{P_{1}}{\rho} + {gZ}_{1}} = {{\frac{1}{2}V_{2}^{2}} + \frac{P_{2}}{\rho} + {gZ}_{2}}} & (1)\end{matrix}$where ρ is the density of the gas flowing in the direction of the arrowsshown in FIGS. 2 and 3, A₁ is the cross-sectional area of each of theareas 112A and 112B that is perpendicular to the plane of the sheet(FIGS. 2 and 3), P₁ is the pressure of the gas in each of the areas 112Aand 112B, V₁ is the speed of the gas, Z₁ is the height from a referencesurface at the center of each of the areas 112A and 112B, A₂ is thecross-sectional area of each of the areas 114A and 114B that isperpendicular to the plane of the sheet (FIGS. 2 and 3), P₂ is thepressure of the gas in the areas 114A and 114B, V₂ is the speed of thegas, and Z₁ is the height from a reference surface at the center of eachof the areas 114A and 114B. Here, since the centers of the areas 112Aand 112B and the corresponding areas 114A and 114B coincide, Z₁=Z₂.Therefore, Formula 1 becomes Formula 2. When Formula 2 is transformed,it becomes Formula 3. $\begin{matrix}{{{\frac{1}{2}V_{1}^{2}} + \frac{P_{1}}{\rho}} = {{\frac{1}{2}V_{2}^{2}} + \frac{P_{2}}{\rho}}} & (2) \\{{P_{1} - P_{2}} = {0.5 \times \rho \times \left( {V_{2}^{2} - V_{1}^{2}} \right)}} & (3) \\{{{Since}\quad V_{1} \times A_{1}} = {V_{2} \times A_{2}}} & (4) \\{{{{and}\quad V_{2}} = {\frac{A_{1}}{A_{2}}V_{1}}},} & (5)\end{matrix}$Formula 6 is established:P ₁ −P ₂=0.5·ρ·V ₁ ²·{(A ₁ /A ₂)²−1}  (6)

When the central lines of the areas 112A and 112B and the correspondingareas 114A and 114B do not coincide, Formula 6 becomes:P ₁ −P ₂=0.5×ρ×V ₁ ²×{(A ₁/A₂)²−1}+ρ×g×(Z ₂ −Z ₁).However, when P₁−P₂is on the order of 100 Pa, ρ×g×(Z₂−Z₁) is12.25×(Z₂−Z₁), so that when Z₂−Z₁ is equal to or less than a value onthe order of 0.1 (10 cm), Formula 6 produces an error on the order of10%, which is not a problem from a practical standpoint.

P₁−P₂ is a difference in pressure between the areas 112A and 112B andthe corresponding areas 114A and 114B. When the gas flow paths 111A and111B are open to the atmosphere in order to set P₂ at atmosphericpressure, it is possible to apply the pressure difference obtained bythe above formula against the weight of the reticle 20 (that is, ingeneral, in the embodiment, G=3.17 and A_(R)=0.152² when G representsthe weight of the reticle and A_(R) is the area of projection of thereticle 20). By setting P₂ at atmospheric pressure and causing the spacearound the reticle 20 to be open, heat will not be confined in the areaaround the reticle 20 as it is in the first embodiment disclosed inJapanese Patent Laid-Open No. 10-214780, thereby making it possible toprevent deformation and distortion of the reticle 20 as a result ofrestricting a temperature rise in the reticle 20.

The relationship between P₁ (upstream gauge pressure) and V₁ (upstreamgas speed) is shown in FIG. 4. An area ratio which is greater than onemeans that the gas flow paths 111A and 111B have shrunk, whereas an arearatio less than one means that they have expanded.

In order to apply a pressure equivalent to the self-weight of thereticle 20 after rewriting Formula 4 using 140 Pa, which is equivalentto the self-weight of the reticle 20, when the gas flow path 111A iscontracted (that is, when A₁>A₂),V ₁=15/{(A ₁ /A ₂)²−1}^(1/2)On the other hand, when the gas flow path 111B is expanded (that is,when A₁<A₂),V ₁=15/{1−(A ₁ /A ₂)²}^(1/2)Referring to FIGS. 2 and 4, when A₁/A₂=2 in the case in which the gasflow path 111A is disposed below the reticle 20, the required gas speedis V₁=8.7 m/sec. Similarly, referring to FIGS. 3 and 4, when A₁/A₂=0.5in the case in which the gas flow path 111B is disposed above thereticle 20, the required gas speed is V₁=8.7 m/sec.

According to the correcting device 100, by blowing gas, such as air ornitrogen, to the gas flow paths having two continuously formed areashaving different cross-sectional areas, a difference in pressure can beproduced between both of the areas as a-result of making use ofBernoulli's theorem. By properly making use of the pressure difference,the correcting device 100 can correct distortion caused by factors otherthan the self-weight of the reticle 20. In addition, the correctingdevice 100 can restrict a temperature rise in the reticle 20, caused byheat of exposure light emitted from the illumination device 10, bycooling the reticle 20 as a result of blowing gas onto the reticle 20.

In FIG. 1, the gas pipe 110, which is recessed above the reticle 20, isused. Therefore, in FIG. 1, the area 114 is provided not only behind thearea 112 but also in front of the area 112 (that is, upstream in termsof the gas that is being blown). Since the cross-sectional area of thearea 112 is smaller than the cross-sectional area of the upstream-sidearea 114, the temperature of the gas in the area 112 can be reduced, sothat the temperature rise in the reticle 20 caused by the exposure heatcan be restricted.

In FIG. 1, the structure shown FIG. 3 can be used instead of thestructure shown in FIG. 2. More specifically, the gas pipe 110 isprovided opposite to the plate 40 in relation to the reticle 20. Ingeneral, a pellicle or a film (not shown) is provided at the plate 40side. The pellicle is a transparent protective film (or a structuralmember thereof) provided within a certain distance from the reticle 20in order to prevent foreign matter from adhering onto the reticle 20.Therefore, by providing the gas pipe 110 opposite to the plate 40 inrelation to the reticle 20, it is possible to prevent the reticle 20from deforming and breaking, when gas flows, by using the pellicle, sothat the reticle 20 can be indirectly protected.

The structures of the gas pipe 110 and the reticle 20 shown in FIG. 1are merely examples. For example, as shown in FIGS. 5 and 6, acorrecting device 100C, including a gas pipe 110C defined by a gas flowpath 111C, having areas 112C and 114C, may be formed by a pair ofcross-sectionally parallel surfaces 116C and 118C in order to cause thereticle 20 to protrude from a bottom surface 118C (or a reticle table)of the gas pipe 110. Here, FIG. 5 is a perspective view of amodification of the correcting device shown in FIG. 1, and FIG. 6 is asectional view thereof. As shown in FIG. 7, the reticle 20 is secured toa reticle chuck 22 through a vacuum hole 23 formed at the reticle chuck22, which is accommodated in a rectangular hole 25 formed in the centerof a rectangular reticle stage 24. By properly setting a height H of thereticle stage 24, a cross-sectional area A₁ of the area 112C shown inFIG. 5 is determined. A cross-sectional area A₂ of the area 114C isdefined by the pair of parallel surfaces 116C and 118C of the gas pipe110C.

The blowing section 120 shown in FIG. 1 blows gas, whose temperature iscontrolled at a certain temperature, towards the scanning direction ofthe reticle stage 24. For example, as shown in FIG. 5, the blowingsection 120 includes a filter 122 and a duct 124. For the gas, air maybe used when the light source 12 is a mercury lamp, while nitrogen orthe like may be used when the light source 12 is a laser. The filter 122is provided at the exit of the blowing section 120 and cleans the gasthat blows from the blowing section 120. For the filter 122, a HEPA(manufactured by Nippon Cambridge Filter Co., Ltd.) may be used. Theduct 124 is connected to an external gas source (not shown) in order tocause the gas to flow into the blowing section 120.

The gas pipe 110 shown in FIG. 1 includes a transmission window 117,formed of a material such as glass that passes exposure light from theillumination optical system 14, at a top surface 116 thereof.

As shown in FIG. 6, it is preferable for the correcting device 100 tofurther include a smoothing section 130, disposed between the areas 112Cand 114C, which smooths the movement of the gas flowing therebetween.The smoothing section 130 can prevent the gas from deviating fromBernoulli's theorem, which would be caused by the gas swirling betweenthe areas 112C and 114C. Although in the embodiment the smoothingsection 130 is formed by a triangular column that is provided at theupstream side and the downstream side of the reticle stage 24, aninclined portion does not have to take the form of a straight line as inthe embodiment. It may take any form, such as a curved form or anarcuate form, as long as it can smooth the movement of the gas.

FIG. 8 illustrates a correcting device 100D, which is a modification ofthe correcting device shown in FIG. 1, in which, similar to the gas pipe110 shown in FIG. 1, a gas pipe 110D, which is recessed above thereticle 20, is formed at a top surface 116D. In the modification, due tothe depth of the recess in the top surface 116D, the cross-sectionalarea of an area 112D can be adjusted. Accordingly, this modification hasthe feature that a height H of the reticle stage 24 shown in FIG. 7 doesnot have to be set at so high a value.

FIGS. 9 and 10 illustrate a correcting device 100E, which is stillanother modification of the correcting device shown in FIG. 1. Morespecifically, a gas pipe 110E is formed so that the reticle stage 24 isaccommodated in a recess 119 formed in a bottom surface 118E (reticletable), and so that the top surface of the reticle stage 24 and the topsurface of the other portions of the bottom surface 118E are at the sameheight. A cross-sectional area A₁ of an area 112E and a cross-sectionalarea A₂ of an area 114E, both of which are illustrated in FIG. 9, aredefined by a stepped portion of a top surface 116E of the gas pipe 110.

The correcting device 100E further comprises a control section 140, amemory 142, and a pressure sensor 150. The blowing section 120, thecontrol section 140, the memory 142, and the pressure sensor 150 form a(feedback) control system. In this modification, the control section 140causes the difference in pressure between the front and back surfaces ofthe reticle 20 to be detected through the pressure sensor 150 in orderto control the blowing section 120 (or a driver (not shown) of theblowing section 120) so that the pressure difference becomes apredetermined value (for example, so that it becomes a value required tocancel the deformation of the reticle 20 caused by its own weight due togravity, or, more specifically, so that it satisfies P_(1−P) ₂=0.5·ρ·V₁²·{(A₁/A₂)²−1}=−G/A_(R). Therefore, the correcting device 100E cancorrect the distortion of the reticle caused by its own weight.

The control section 140 is connected to the pressure sensor 150 in orderto control, for example, the blast volume, and the gas speed and the gastemperature at the blowing section 120 based on the detection results ofthe pressure sensor 150. The control section 140 is also connected tothe memory 142, so that the memory 142 can store the method ofcontrolling the blowing section 120 carried out by the control section140 and/or the data used for the method. The memory 142 may be aread-only memory (ROM), a random-access memory (RAM), other such storagedevices. In this modification, the control section 140 is a controlsection of the exposure apparatus 1. However, if necessary, this controlsection 140 may be a control section of an external device, theillumination device 10, and the projection optical system 30. Inaddition, separate control sections may be provided for these componentparts.

The pressure sensor 150 comprises a sensor 152, disposed at the frontside of the reticle 20 inside a gas flow path 111E, and a sensor 154,disposed at the back side of the reticle 20 below a bottom surface 118Eof the gas pipe 110E. For the pressure sensor 150, sensors of anystructure known in the industrial field, such as a strain gauge, a loadcell, a piezoelectric device, a pressure electrically conductive sheet,a pressure sensitive polymer, a photodiode, an electrostatic capacitive(differential pressure) sensor, a Bourdon tube, a bellows, a diaphragm,or a torsion bar may be used. The structures and operations of thesetypes of sensors are well known, and will not be described in detailbelow.

FIG. 11 is an external perspective view of a correcting device 100F,which is still another modification of the correcting device 100 shownin FIG. 1. The correcting device 100F is similar to the correctingdevice 100E, but differs from it in that, unlike the area 114E thatspreads vertically with respect to the area 112E, an area 114F spreadstowards the left and right with respect to an area 112F. In other words,a top surface 116F of a gas flow path 110F (not shown) is maintainedhorizontally with respect to the areas 112F and 114F. By combining thestructures shown in FIGS. 9 and 11, the area 114F may spread in theupward and downward directions and towards the left and right withrespect to the area 112F.

In the present invention, it does not matter what scanning method isused on the reticle 20, so that, for example, as shown in FIGS. 12 to15, the present invention may be applied to a scanning exposureapparatus 200. Referring to FIGS. 12 and 13, the correcting device 100Fis used with the reticle 20 that is scanned in synchronism by a pair oflinear motors 204 and 227, which can move perpendicular to each other.FIG. 13 shows a state in which the reticle 20 has moved towards the leftfrom its position shown in FIG. 12.

Hereafter, with reference to FIGS. 14 and 15, the exposure apparatus 200will be described. FIG. 14 is a schematic side view of the exposureapparatus 200, and FIG. 15 is an external perspective view of theexposure apparatus 200. Through a projection optical system 202, theexposure apparatus 200 projects a portion of the circuit pattern of thereticle 20 disposed on a reticle stage 201, which holds the reticle 20and which can be used for performing a scanning operation in the Ydirection, onto a wafer W disposed on an XY stage 203. The exposureapparatus 200 is a step-and-scan exposure apparatus which is used toproject the pattern of the reticle 20 onto the wafer W by exposure as aresult of scanning the reticle 20 and the wafer W in the Y direction insynchronism with each other with respect to the projection opticalsystem 202 and which interposes stepwise movements in order to applyscanning exposure light to a plurality of shots on the wafer W.

The reticle stage 201 is driven in the Y direction by the linear motors204 and 227. An X stage 203 a of the wafer stage 203 is constructed sothat it is driven in the X direction by a linear motor 205, and a Ystage 203 b is constructed so that it is driven in the Y direction by alinear motor 206. The synchronized scanning operation of the reticle 20and the wafer W is carried out by driving the reticle stage 201 and theY stage 203 b in the Y direction at a fixed speed ratio (for example,4:-1, where the - sign means opposite direction) while laserinterferometers 222 and 223 monitor the locations of the reticle stage201 and the Y stage 203 b in the Y direction. The wafer W is movedstepwise in the X direction by the X stage 203 a.

The wafer stage 203 is provided on a stage table 207, which is supportedon, for example, the floor at three points through three dampers 208.The reticle stage 201 and the projection optical system 202 are providedon a telescopic surface plate 209, which is supported through threedampers 211 and column supports 212 on a base frame 210 disposed on, forexample, the floor. Although the dampers 203 are active dampers thatactively deaden or isolate vibration in six axial directions, they maybe passive dampers. In addition, dampers do not need to be used tosupport the telescopic surface plate 209.

At three points between the telescopic surface plate 209 and the stagetable 207, the exposure apparatus 200 includes distance-measuring means,such as measurement laser interferometers or microcomputers. Lightprojecting means 221 and light-receiving means 222 form a focus sensorfor detecting whether or not the wafer W on the wafer stage 203 ispositioned at a focal plane of the projection optical system 202. Morespecifically, the light-projecting means 221, secured to the telescopicsurface plate 209, projects light onto the wafer W from an obliquedirection, and the light-receiving means 222 detects the location of thereflected light in order to detect the location of the surface of thewafer W in the optical axis direction of the projection optical system202.

In the structure, transporting means (not shown) transports the wafer Wonto the wafer stage 203 via a transportation path between the twocolumn supports 212 at the front portion of the exposure apparatus 200.When a predetermined alignment is completed, the exposure apparatus 200transfers the pattern of the reticle 20 onto a plurality of exposureareas of the wafer W by exposure while it repeats scanning exposureoperations and causes stepwise movements to be repeated. In the scanningexposure operation, the reticle stage 201 and the Y stage 203 b aremoved at a predetermined speed ratio in the Y direction (scanningdirection). Using slit-shaped exposure light, the pattern on the reticle20 is scanned, and the wafer W is scanned using the projection image ofthe pattern in order to project the pattern of the reticle 20 onto apredetermined exposure area of the wafer W by exposure. During thescanning exposure operation, the height of the surface of the wafer W ismeasured by the focus sensor. Based on the measured value, the heightand tilt of the wafer stage 203 are controlled in real time in order tocorrect the focus. After completion of a scanning exposure operation onone exposure area, by driving the X stage 203 a in the X direction inorder to move the wafer W stepwise, another exposure area is positionedat a scanning exposure starting location and is, then, subjected toscanning exposure. By combining the stepwise movements in the Xdirection and the movements for performing scanning exposure in the Ydirection, in order to allow the exposure operations to be successivelyperformed efficiently with respect to the plurality of exposure areas onthe wafer W, the location of each of the exposure areas, scanning in the+Y or −Y direction, the order in which each exposure area is exposed,and the like, are set.

In the exposure apparatus 200 shown in FIG. 14, light that has beenemitted from a laser interferometer light source (not shown) is causedto enter the Y-direction laser interferometer 224. The light that hasentered the Y-direction laser interferometer 224 is divided by a beamsplitter (not shown) inside the laser interferometer 224 into light thatis directed towards a fixed mirror (not shown) disposed inside the laserinterferometer 224 and light that is directed towards a Y-directionmoving mirror (not shown). The light that is directed towards theY-direction moving mirror passes through a Y-direction lengthmeasurement optical path (not shown), and, then, impinges upon theY-direction moving mirror secured to the reticle stage 201. Here, thelight that is reflected passes again through the Y-direction lengthmeasurement optical path, returns to the beam splitter inside the laserinterferometer 202, and is superimposed on the light reflected at thefixed mirror. At this time, by detecting changes in the interference oflight, the distance of movement in the Y direction is measured. Theinformation regarding the distance of movement measured in this way isfed back to a scanning control device (not shown), which controls thepositioning operation of a scanning location of the reticle stage 201.

The reticle 20 is deformed as a result of being heated by the exposurelight from the illumination device 10. In the present invention, it ispossible to correct both thermal deformation of the reticle 20 andflexure of the reticle 20 caused by its own weight. Hereafter, anexample of correcting the deformations of the reticle 20 will be givenwith reference to FIG. 16. FIG. 16 is a schematic block diagram of adetecting section 150 that detects any distortion of the reticle 20. Thereticle 20 is secured to the reticle chuck 22 through a suction pad 21.The reticle 20 is distorted by a flexure amount δ caused by its ownweight, heat, and other factors. The detecting section 150 comprises alight-emitting section 152, lenses 154 and 156, and a light-receivingsection 158. In this example, the light-emitting section 152 and thelight-receiving section 158 form a light-reflective photo-interrupter. Alight-emitting diode (LED), a laser diode (LA), or the like may be usedfor the light-emitting section 152. A photodiode, phototransistor, aphoto IC, or the like may be used for the light-receiving section 158.The light-emitting section 152 illuminates a pattern formed on thesurface of the reticle 20. Light reflected therefrom is detected by thelight-receiving section 158 in order to detect the flexure amount δ ofthe reticle 20. The detection results provided by the light-receivingsection 158 is transmitted to, for example, the control section 140shown in FIG. 10. The control section 140 makes use of such results tocontrol the blowing section 120. The control section 140 controlsfeedback of the blowing section 120 so that the flexure amount δ of thereticle 20 becomes zero in order to correct the distortions of thereticle 20.

In the exposure, light beams emitted from the light source 12 are usedto subject the recticle 20 to, for example, Koehler illumination by theillumination optical system 14. Since the exposure apparatus 1 makes itpossible to reduce or remove the distortions of the reticle 20, thepattern of the reticle 20 can be transferred onto the resist with highprecision, so that a high-quality device (such as a semiconductordevice, a liquid crystal display (LCD) device, an image pickup device(including a charge-coupled device (CCD)), and a thin-film magnetichead) can be provided.

Referring to FIGS. 17 and 18, an embodiment of a device productionmethod using the above-described exposure apparatus 1 will be described.FIG. 17 is a flowchart used to illustrate the production of a device(such as a semiconductor chip of, for example, an integrated circuit(IC) or a large-scale integrated circuit (LSI), an LCD, and a CCD).Here, an example of producing a semiconductor chip will be described. InStep 1, a circuit pattern is designed for the device. In Step 2, a maskhaving the designed circuit pattern formed thereon is produced. In Step3, a wafer is produced, using silicon or other materials. In Step 4(wafer process or pre-processing step), the mask and the wafer are usedto actually form the circuit on the wafer using lithography techniques.Then, in the following step, Step 5, (post-processing step), the waferproduced in Step 4 is formed into a semiconductor chip, wherein assembly(dicing, bonding), packaging (of the chip), and the like are performed.In Step 6, the semiconductor device produced in Step 5 is inspected byconducting operation confirmation tests, durability tests, and the like.Thereafter, in Step 7, the finished semiconductor device is shipped.

FIG. 18 is a detailed flowchart of Step 4 (the wafer process). In Step11, the surface of the wafer is oxidized. Then, in Step 12(chemical-vapor deposition (CVD) step), an insulation film is formed onthe wafer surface. In Step 13, an electrode is formed on the wafer by,for example, evaporation. In Step 14, ions are implanted into the wafer.In Step 15, a photosensitization agent is coated onto the wafer. In Step16, the mask circuit pattern is printed onto the wafer by exposure usingthe exposure apparatus 1. In Step 17, the exposed portion of the waferis developed. In Step 18, portions other than where the developed resistimage is formed are etched. In Step 19, unwanted resist is removed fromthe wafer after etching. Multiple circuit patterns are formed on thewafer by repeating the above-described steps. By virtue of thisembodiment of the device production method, devices having a higherquality than conventional devices can be produced.

Except as otherwise discussed herein, the various components shown inoutline or in block form in the Figures are individually well known andtheir internal construction and operation are not critical either to themaking or using or to a description of the best mode of the invention.

While the present invention has been described with reference to whatare presently considered to be the preferred embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments. On the contrary, the invention is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims. The scope of the following claims is to beaccorded the broadest interpretation so as to encompass all suchmodifications and equivalent structures and functions.

1-16. (canceled)
 17. A method of producing a device, comprising thesteps of: blowing gas to a gas flow path including a first area and asecond area, the first area being formed above a reticle having formedthereon a pattern that is projected onto a material to be processed inorder to form an image of the pattern on the material to be processed,and the second are being connected to the first area, having across-sectional area that is different from that of the first area, andnot being disposed in line with the reticle; subjecting the material tobe processed to a projection exposure operation using the reticle; andperforming a predetermined processing operation on the material that hasbeen subjected to the projection exposure operation to produce a device.18. A method of producing a device according to claim 17, furthercomprising detecting distortion of the reticle and controlling the stepof blowing gas so that distortion of the reticle is reduced based on thedetection of the distortion of the reticle. 19-36. (canceled)